Aquatic facilities are a primary example of the need for proper water conditioning. When water is used for swimming, it must meet stringent health standards. Once the water is preconditioned, it is most economical to recirculate the water through water conditioning equipment to maintain such standards. For this reason, the water is commonly treated with various chemicals. A known problem with water conditioning chemicals is that many of them are dependent on the maintenance of an appropriate pH for proper operation. In many circumstances the chemical itself will cause an alteration of the pH upon its introduction into the water.
Calcium hypochlorite is an oxidizer that is commonly accepted for use in a variety of aqueous systems, including the aquatic environment. However, effective application of calcium hypochlorite is highly dependent on the concentration of alkalinity in the supply water and the treated water pH. Generally speaking, supply water having a high concentration of alkalinity with the addition of calcium hypochlorite causes hard water scaling. This scaling often occurs at the injection point and throughout the feed line. When such scaling occurs, it makes it necessary to routinely remove the scale by disassembly of the equipment and washing in an acid bath.
Calcium hypochlorite is commonly manufactured in the form of pellets and inserted into a water-treatment application by dissolving the pellets before injection. The calcium hypochlorite pellet, in its commercially available form, generally consists of the following constituents.
Calcium hypochlorite 69-71% PA1 Water 5.5-8.5% PA1 Sodium Chloride 14-17% PA1 Calcium Hydroxide 2-2.5% PA1 Calcium Carbonate 2-2.5% PA1 Other Soluble Calcium Salts 1-2.5%
Two types of chemical feeders are commonly used for dissolving calcium hypochlorite pellets. An erosion feeder immerses calcium hypochlorite pellet s into a solution of water thereby allowing the water to dissolve the pellets, the water is then transferred into the water treatment application. Alternatively a feeder may consist of an apparatus wherein water is sprayed onto the pellets, either from above or below. The water feed contains some alkalinity and typically has a pH of around 7.5. The alkalinity will precipitate out at a pH of around 8.3. The problem with calcium hypochlorite is that it includes hydrated or slaked lime--calcium hydroxide (Ca(OH).sub.2) which can elevate the pH of water. Typically the water discharged from the feeder has a pH of about 10.5. due to the dissolution of calcium hydroxide. In the presence of calcium and alkalinity, an elevation of the pH leads to calcium carbonate scaling which results in clogging of the feeders.
A small amount of scale can quickly restrict or stop the output of a chemical feeder. In a swimming pool or spa, the fluctuation of pH and its effect on chlorine feed can quickly lead to expensive maintenance problems and/or unsanitary conditions. More importantly, such problems can result in a safety concern to those servicing, as well as using, the facilities. The actual rate at which the restriction develops is largely dependent upon the concentration of alkalinity in the water. Generally, the higher the alkalinity, the faster the restriction develops. Because of the formation of this undesired calcium carbonate scale, maintenance of chemical feed systems in such a water treatment application can be high and is often considered unacceptable. Frequent cleaning of feeders and downstream equipment may be necessary to remove the scale. For this reason, it is typically recommended by suppliers of calcium hypochlorite to use HCl for controlling pH of pool water, because it destroys alkalinity. This often creates additional problems because HCl is a strong acid and dangerous fluctuations in pH can occur very quickly, especially if water flow is restricted at some point.
Thus, what is lacking for water treatment applications is a safe and convenient means for eliminating or reducing calcium carbonate scaling in the feed lines and injection points of calcium hypochlorite based water treatment systems.